The effect of different flow fields on particle size distribution (PSD) in suspensions using modified population balance/DEM

Suspensions are among most important systems that widely used in many applications. Depending on conditions, some phenomena such as aggregation, flocculation and settling can occur in the suspensions. In the case of dynamic processing of suspensions, there is always a competition between two major phenomena: formation and breakage of aggregates/agglomerates. In the present work, the modified population balance equations (PBEs) were solved using the non-uniform discretization scheme and considering breakage process in two different flow fields, the shear and elongational flow fields. Considering the agreement of obtained results using PBEs with the results derived from 2-D discrete element method(DEM), a power-law relationship is proposed for modifying flocs break-up function to consider the elongational flow field’s and an exponential kernel is considered for shear breakage effect. The aggregate break-up process evaluated in terms of weighted average particle number in aggregates, , and volume mean diameter, d[4,3]. By increasing the extent of the elongational rate in the flow field, the breakage process was increased, and consequently, the mean particle size shifts toward finer particles. Therefore, both and d[4,3] dropped faster than the shear slow field. Moreover, the break-up process in elongational flow field is more sensitive to the variation of fractal dimension in comparison with shear flow field.

Keywords:

Agglomerate , Particle Size Distribution (PSD) , Discrete Element Method (DEM) , Population Balance Model (PBM) , Elongational Flow Field